Hi!
On 11/02/16 21:53, Yang Shi wrote:
> Switching between stacks is only valid if we are tracing ourselves while on
> the
> irq_stack, so it is only valid when in current and non-preemptible context,
> otherwise is is just zeroed off.
Given it was picked up with CONFIG_DEBUG_PREEMPT:
Fixes: 132cd887b5c5 ("arm64: Modify stack trace and dump for use with
irq_stack")
> Signed-off-by: Yang Shi <[email protected]>
> ---
> arch/arm64/kernel/stacktrace.c | 13 ++++++-------
> arch/arm64/kernel/traps.c | 11 ++++++++++-
> 2 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 12a18cb..d9751a4 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -44,14 +44,13 @@ int notrace unwind_frame(struct task_struct *tsk, struct
> stackframe *frame)
> unsigned long irq_stack_ptr;
>
> /*
> - * Use raw_smp_processor_id() to avoid false-positives from
> - * CONFIG_DEBUG_PREEMPT. get_wchan() calls unwind_frame() on sleeping
> - * task stacks, we can be pre-empted in this case, so
> - * {raw_,}smp_processor_id() may give us the wrong value. Sleeping
> - * tasks can't ever be on an interrupt stack, so regardless of cpu,
> - * the checks will always fail.
> + * Switching between stacks is valid when tracing current and in
> + * non-preemptible context.
> */
> - irq_stack_ptr = IRQ_STACK_PTR(raw_smp_processor_id());
> + if (tsk == current && !preemptible())
> + irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
> + else
> + irq_stack_ptr = 0;
>
> low = frame->sp;
> /* irq stacks are not THREAD_SIZE aligned */
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index cbedd72..7d8db3a 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -146,9 +146,18 @@ static void dump_instr(const char *lvl, struct pt_regs
> *regs)
> static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> {
> struct stackframe frame;
> - unsigned long irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
> + unsigned long irq_stack_ptr;
> int skip;
>
> + /*
> + * Switching between stacks is valid when tracing current and in
Nit: Two spaces: "between[ ][ ]stacks"
> + * non-preemptible context.
> + */
> + if (tsk == current && !preemptible())
> + irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id());
> + else
> + irq_stack_ptr = 0;
> +
> pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
>
> if (!tsk)
>
Neither file includes 'linux/preempt.h' for the definition of preemptible().
(I can't talk: I should have included smp.h for smp_processor_id())
Acked-by: James Morse <[email protected]>
Tested-by: James Morse <[email protected]>
Thanks!
James
